The present invention is related generally to vehicle wheel tire changing systems, and in particular, to an improved vehicle wheel tire changing system configured to detect the presence of a tire pressure monitoring system sensor mounted within a vehicle wheel assembly prior to altering the mounting of a tire on an associated wheel rim.
Modern vehicle wheel assemblies on most motor vehicles today consist of a pneumatic tire mounted or seated on a wheel rim, such as shown in FIG. 1. The tire is secured to the wheel rim by forces exerted between the inner peripheral edges of the tire, i.e. the beads, and the mating surfaces of the wheel rim, i.e. the bead seats. Pressurized air contained within the toroidal volume defined between the tire and wheel rim supports the tire against the weight of the vehicle. Tire pressure monitoring systems associated with motor vehicles such as passenger cars and light trucks are designed to provide a warning to drivers if the pressure level of air within tire on the vehicle becomes significantly decreased during operation. There are two types of tire pressure monitoring systems currently in use. The first is an indirect system, which relies upon rotational speed measurements acquired by the vehicle anti-lock braking system sensors during vehicle operation. A tire which is significantly deflated relative to the remaining tires on the vehicle will have a smaller rolling radius, and therefore will rotate faster. Significant differences in vehicle wheel rotational speeds are interpreted as being indicative of an under-inflated tire by an indirect tire pressure monitoring system, and a suitable warning is provided to the vehicle operator. However, indirect tire pressure monitoring systems cannot identify small changes in tire pressures, and are incapable of identifying situations in which all of the vehicle wheels are under-inflated.
The second type of tire pressure monitoring system is a “direct” system, in which each wheel assembly of the vehicle is equipped with a tire pressure sensor disposed in an operative relationship to the pressurize air contained between the tire and wheel rim. For example, as is shown in FIG. 2, a tire pressure sensor may be strapped about the surface of the vehicle wheel rim, such that the tire pressure sensor is disposed within the volume defined by the tire about the wheel rim. Alternatively, as shown in FIG. 3, the tire pressure sensors may be coupled to, or associated with, the valve stem of the vehicle wheel assembly. Typically, tire pressure sensors are configured to transmit data using high-frequency radio waves in the preferred range of 300 MHz-450 MHz to a common control unit. Specific frequencies such as 303 MHz, 315 MHz, 418 MHz, 434 MHz, and optionally 868 MHz are generally employed by tire pressure monitoring systems currently in use. The common control unit is configured to process the received data and provide the operator with a suitable display of vehicle wheel tire pressures. An exemplary “direct” tire pressure monitoring system is manufactured and sold by Smartire Systems, Inc. of Richmond, Calif.
To prevent cross-talk between tire pressure monitoring systems of nearby vehicles, each tire pressure sensor is configured to transmit a unique identification code together with the tire pressure data signal. Depending upon the configuration of the particular “direct” system, and the signal range, the tire pressure monitoring system may be utilized to further monitor pressure in a vehicle's spare tire, or pressure in the tires of a towed trailer.
To provide a vehicle operator with useful information regarding tire pressure levels, a “direct” tire pressure monitoring system must provide the operator with a means to identify which monitored tires have reduced tire pressure. Identifying the vehicle wheel location for each tire pressure sensor in a vehicle tire pressure monitoring system may be done manually or automatically. Manual systems require some form of operator interaction, such as by physically installing predetermined tire pressure sensors in tires positioned in predetermined locations about a vehicle. Alternatively, each tire pressure sensor can be identified by a unique indicator to the common control unit, for example, a color-coded marking on the tire valve stem. When a low tire pressure condition is detected by one of the tire pressure sensors, the control unit displays a corresponding color to the vehicle operator, requiring the operator to inspect the vehicle wheels to locate the corresponding color marking. Manual systems often require the operator to retrain or reposition the tire pressure sensors following a vehicle wheel rotation or service, a time-consuming and error-prone procedure.
Alternatively, tire pressure monitoring systems may be configured to automatically identify the corresponding tire locations associated with each tire pressure sensor in the system. These “automatic” systems typically provide a trigger mechanism or signal to activate each tire pressure sensor's transmitter in a predetermined sequence. The unique identification associated with each transmitter is stored as it is received in the predetermined sequence, thereby associating each tire pressure sensor with a known tire location. For some systems, the tire pressure sensors include a magnetic switch which is activated or triggered by the proximity of a magnetic field to direct the tire pressure sensor to transmit the unique identification. Alternate systems incorporate a radio-frequency receiver into each of the tire pressure sensors. Each of the receivers responds to a specific trigger signal, typically around 125 MHz, to transmit the associated tire pressure sensor's unique identification. While the programming of an “automatic” system remains time consuming, the need to physically reposition each tire pressure sensor following a tire rotation or tire service is eliminated, saving significant time during a vehicle service procedure.
Still other tire pressure monitoring systems are fully automatic in terms of locating each of the tire pressure sensors associated with a vehicle. These systems typically employed radio-frequency antenna disposed in proximity to the vehicle wheels, and uniquely identify each individual tire pressure sensor by monitoring the strength of the signals emitted by each tire pressure sensor, specific antenna identification codes, or specific radio-frequency variations on the order of a few KHz, associated with each tire pressure sensor.
During a tire service procedure, it may be necessary to utilize a vehicle wheel tire changing system to remove a tire from a wheel rim, or to “break” the seated connection between the tire and wheel rim. A vehicle wheel tire changing system typically employs hydraulic or pneumatically actuated clamps and arms to secure and compress the tire during these procedures, thereby disassociating the tire beads or lips from the beadseat of the wheel rim. Significant forces are exerted on the tire and wheel rim during this process. If a tire pressure sensor associated with a tire pressure monitoring system is installed about the wheel rim, within the volume defined by the tire, it is possible for a vehicle wheel tire changing system to damage or destroy the tire pressure sensor if care is not taken during the tire service procedure.
Currently, an operator of a vehicle wheel tire changing system must either know in advance that a tire pressure sensor is present in a wheel assembly undergoing a tire service, or carry out a difficult visual inspection during the tire service to identify the presence of a tire pressure sensor. Accordingly, it would be advantageous to provide a vehicle wheel tire changing system with a means to detect the presence of a tire pressure sensor associated with a tire pressure monitoring system in a vehicle wheel assembly prior to removing or altering the mounting of the tire about the wheel rim. It would be further advantageous to provide a vehicle wheel tire changing system with a means to determine the operational condition of a detected tire pressure sensor prior to removal or altering of the mounting of the tire about the wheel rim.